GB2201162A - Electrode boat apparatus for plasma enhanced chemical vapour processing semiconductor wafers - Google Patents

Description

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v 22- 0 116 2 ELECTRODE BOAT APPARATUS FOR PROCESSING SEMICONDUCTOR WAFERS OR THE LIKE The present invention relates generally to an apparatus for processing semiconductor wafers and, more particularly, relates to a wafer boat assembly used to hold semiconductor wafers or the like within externally excited, chemical reaction systems wherein the reactant material flows over the wafers or workpieces which are held with their broad surfaces perpendicular to the flow of the reactant material.

Plasma enhanced Chemical vapor reactors are known in the art wherein the plasma reactant gas or gasses flow perpendicular to the broad surfaces of serially arranged workpieces. For instance, U.S. Patent No. 4,401,507 issued to George M. Engle et al on August'30, 1983, which is expressly incorporated herein by reference made thereto, is representative of the type of plasma chemical vapor reactor to which the present invention is applicable. The chemical reactor systems of the type disclosed in the U.S. Patent No. 4,401,507, utilize an evacuable envelope retained in a furnace. A boat assembly that is removably inserted into the tabular envelope is used to hold workpieces perpendicular-to the flow of the gas reactants that are passed through the tubular envelope during the deposition process onto the workpieces. Process uniformity is of.great concern and an ultimate 1 fj goal in chemical vapor reactor systems. It is desirable to deposit a substantially uniform thickness of the film onto the workpieces. Ideally, the film thickness on the workpieces processed in the chemical reactors should have a maximum of-4-3% deviation wafer to wafer from,.one end of the loaded boat assembly to the other. In addition, it is desirable to be able to process as-many workpieces as possible during each chemical vapor deposition process to maximize wafer throughput.

U.S. Patent No. 4,610,748, issued to George M. Engle et al on September 9, 1986 and entitled "Apparatus for Processing Semiconductor Wafers or the Like," which is also incorporated herein by reference made thereto, gives a detailed description of a boat assembly suitable for holding discshaped workpieces, such as-semiconductor wafers, for processing in plasma enhanced chemical vapor reactors. While the boat assembly described in U. S. Patent 4,610,748 represents a significant advance over known prior art, such a configuration is capable of improvement with respect to ease of disassembly for component replacement, assembly distortion during temperature excursions and component interchangeability between different sized assemblies used in diverse applications. It is also desirable to make a positive and reliable electrical contact to the electrode plates

U t_ I1 - which support the workpieces. It is further very desirable to have a boat assembly which minimizes particulate contamination during processing.

Thus a need exists for an improved apparatus capable of being utilized in contemporary plasma enhanced chemical vapor deposition reactors which maintain process uniformity deviations below 4- 3% while, at the same time, allowing greater wafer throughput than is presently possible with conventional boat assemblies.

Accordingly, it is an object of the present invention to provide an improved boat apparatus for use in the processing of workpieces.

It is another object of this invention to,rovide an apparatus for improved process uniformity in an externally excited chemical reaction process.

Yet another object of the invention is to provide an Apparatus for improved uniformity of etch rate, etch profile and selectively in an externally excited chemical reaction process.

Still another object of this invention is to provide an apparatus for permitting higher deposition rate using less peak power in an-externally excited chemical reaction process.

A further object of this invention is io provide a boat assembly for use in a chemical reaction pr9cess which allows a large number of workpieces to be processed in a chemical reaction process with improved process uniformities.

It is still a further object of this invention to provide an electrode boa t assembly for holding a large number of semiconductor wafers with their broad surfaces perpendicular to the flow of a reactant during processing in a chemical reaction process such that improved process components, high deposition rates and the use of less peak power are achieved.

It is yet another object of this invention to provide an electrode boat assembly which permits positive and reliable electrical contact to disc plate electrodes while permitting easy assembly and disassembly, yet which exhibits-improved resistance to degradation during thermal excursions typically encountered in a processing sequence.

In accordance with the above and other objects hereinafter disclosed, there is provided an electrode boat assembly comprising a pair of conductive support members. each member having a plurality of interleaved electrode plates held thereto, and each member beingcovered by insulating means except where electrical connected to an electrode plate. Each conductive support member, which is preferably coaxially surrounded by the insulating means, has a coefficient of thermal expansion which is chosen to substantially match that of the - t U fl fm c insulating means. Compression fittings allow for positive electrical contact between the electrode plate and the conductive support member.

The invention will now be described further, by way of example only, with reference to the accompanying -drawings in which:- Fig. 1 is a side elevational partial cross.sectional view of a portion of the electrode boat assembly portion of the electrode boat assembly according to the present invention; Fig. 2 is a view of the electrode boat assembly portion along line 2-2 of Fig. 1; Fig. 3 is a side elevation, partly in cross section, of a portion of the electrode boat assembly according to another preferred embodiment of the present inventione, Fig. 4 is an enlarged side elevational view, partly in section, showing another embodiment of a single, integral conductor-rod assembly that can be used in place of the conductor rod screw or bolt and nut elements depicted in Fig. 1.

Referring now to the drawings, and particularly to Fig. 1,, there is shown a Portion of an electrode boat assembly suitable for use with the vapor processing apparatus as described in U.S. Patent 4,223,048. The apparatus described in U.S. Patent 4,223,048 may be but one of a variety of-continuous or-pulsed RP plasma enhanced \-'i or other chemical processing systems to which the electrode boat assembly according to the present invention may be applied..

The'electrode boat portion shown in Fig. I comprises 5 a plurality of interleaved electrodes 22 and 24. Electrodes 22 and 24 are preferably constructed of graphite or other conductive material resistant to high temperature chemical environments. E lectrodes 22 are electrically common, as are electrodes 24, so that an RF plasma may be set up in'the space between each alternating pair of electrodes 22 and 24. Workpieces or semiconductor wafers 44 that are to be processed may be mounted on both faces of each electroae' 22 and 24. The workpieces may be supported for example, by pegs 16, which may be wedge-shaped.and are preferably.constructed of the same material as electrodes 22 and 24. The electrode assembly is supported by a plurality of longitudinal support members including rods'8a and 12 and coaxial spacers 10a and 14. The extremities (not shown) of the longitudinal support members extend to terminal end members (not shown) which provide mechanical support and/or electrical contact, as described more completely in U.S. Patent 4,610,748, hereinbefore incorporated by reference. Rod 12 in Fig. 1 is an insulating support member extending through a bore in each of the electrodes 22 and 24. Rod 12 preferably comprises alumina, and is coaxially U1 r surrounded by a plurality of insulating sleeves 14 also preferably of alumina, which provide further support and maintain the desired spacing between the plurality of electrodes 22 and 24.

Rod'8a co mprises a conductive material for making electrical contact between electrode plates 22. Rod8a passes through A bore in a conductive screw 32 which passes through electrode 22. Positive electrical contact to the electrode 22 is achieved by means of, for example, nut 34 which, together with screw'32, provides a compression contact to electrode plate 22. Screws 32 may be secured to conducting rod8a by set screws 36. Insulating sleeves 10a maintain interelectrode spacing and prevent spacious plasma formation at-locations away from between workpieces 44. Such spurious plasma formation can seriously degrade the uniformity of films deposited on workpieces 44.

It is a particular feature of the present invention that conductive rod'8a has substantially the same coefficient of thermal expansion as the sleeves 10a and, preferably, the same as insulating rod 12 and sleeves 14. By providing substantially matched thermal expansion coefficients., shifting and distortion of electrode plates 22 and 24-is largely obviated during the large temperature excursions encountered in the vapor-processing apparatus., Equally important., particulate contamination, which can be U incorporated in the films to be deposited on the workpieces 44, is dramatically reduced. In the embodiment of Fig. 1, a preferred material for electrode rod-8a is a fine-grain, high-strength graphite material with a coefficient of thermal expansion of about 7.8 parts per million per centigrade degree. Such a material is available from the Poco Division of Unocal Corporation and is an excellent thermal match to the preferred alumina material of rod 12 and sleeve spacers 10a and 14.

As shown in Figure 4, if desired,the nut 34 and the screw or, bolt 32, together with the conductor rod 8 (see Figure 1), can be made into a single integral piece, namely a conductor rod assembly 18, and effectively r eplace the function of the rod 8 while still maintaining all other physical constraints or parameters.of the rod 8. The conductor rod assembly 18, comprises a conductive material for making electrical contact between electrode plates 22, and includes a bolt portion32a, a nut portion 34a, and a spacer pqrtion 26. One conductor rod assembly 18 is operably coupled to at least one other conductor rod assembly to form a continuous conductive line of any desired length (as determined by the amount or number of selected conductor rod assemblies 18 that are chosen to assemble or connect together as shown in Fig. 4) throughout the approximate length of the boat assembly.

Fig. 2 shows a.view of the_electrode boat portion of z 1 j i il C1 Fig 1. A notch in the lower left hand portion of electrode plate 22 is employed to allow a second conducting rod8b and insulating sleeve spacer 10b to pass through the electrode plate 22 without making electrical contact. it will be appreciated by those skilled in the art,, that a- similar notch Will be used,in each of the electrode plates, with electrode plates 2.4 having the notch in the lower right hand corner, to permit contact to alternaing electrode plates by each electrode rod'8a and8b. The use of electrode rod'8a or 8b and two insulating rods 12 with their associated sleeve spacers provide three points of support for each electrode plate. Additionally insulating rods and spacer sleeves may be provided for.very large electrode plates.

Fig. 3 shows a portion.of an electrode boat according to another preferred embodiment of this invention. This embodiment is substantially. similar to that of Fig. 11 except that the electrode rod 42, which replaced electrode rod8a of Fig. 1, is threaded alumina metallized with nickel for conductivity. Spacer sleeve 40, also of aluminal separates alternating pairs -of electrode plates 22, and a nickel nut 34 is used to provide positive electrical contact between electrode rod 40 and electrode plates 22. Again, a substantial thermal expansion coefficient match is achieved between the electrode rod ki - 10 42 and spacer sleeve 40.

In either of the preferred embodiments, the use of the supporting rods, insulating sleeve spacers, and threaded contact assemblies allow rapid assembly of the boat and rapid disassembly for Pleaning or replacement of defectiVe elements. Also, this type of assembly is adaptable to electrode plates of any size, so that most components are interchangeable. By use of electrode boat assemblies according to this invention, deposition uniformities of better than 2% (across a workpiecet from workpiece-toworkpiece, and run-to-run) 3ave been achieved.

Additionally, there is substantial absence of particulate contamination.

The invention is not limited to the detail of the embodiments hereinbefore described, since alternatives will readily present themselves to ones skilled in the art. Thus, for example, the conductive rods inside the alumina spacer sleeves could be Kovar or Rodar alloys as well as the preferred graphite or metallized alumina materials.

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Claims (7)

1. CLAIMS: 1. In a chemical vapor processing apparatu.9 for processing

   workpieces in a plasma reaction within an evacuable envelope for containing the chemical.vapor and the workpieces, an electrode boat assembly removably insertable within the envelope and comprising: a plurality of electrically conductive electrodeplate members, said electrode plate members being interleaved with respect to each other; at least one insulating rod passing through said plurality of electrode plate members, at least one conducting rod passing through said. plurality of electrode plate members, said rod electrically contacting every other one of said plurality of electrode members; and a plurality of insulating sleeve means over saidinsulatingrod and over said conductive rod between said plurality of electrode members for supporting and spacing said plurality of electrode members, wherein said insulating rod, said conductive rod, and said plurality of insulating sleeve means all have substantially the same coefficient of thermal expansion.
2. 2. The boat assembly according to claim 1, wherein said conducting rod comprises a graphite, and said plurality of insulating sleeve means comprises alumina.
3. 3. The boat assembly according to claim 1, wherein said 2 1 1% - 12 conducting rod comprises metallized alumina, and said plurality of insulating sleeve means comprise alumina.
4. 4. The boat assembly according to claim 1, wherein said conducting rod comprises Kovar.
5. 5. The boat assembly according to claim lp wherein said conducting rod comprises Rodar.
6. 6. The boat assembly according to any one of the preceding claimst further comprising threaded means over said conducting rod for making positive electrical 10 contact to said electrode plates.
7. 7. In or for a chemical vapor processing apparatus for processing workpieces on a plasma reactor within an evacuatable envelope for containing thp.chemical vapor and the wokkpieces an electrode boat assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

   Published 1988 at The Patent Office, State House, 65/71 High Holborn, London WClR 4TP. Further copies maybe obtained from The Patent Office, Wes Branch, St Maxy Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.

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